Kyriazakis I, Anderson D H, Oldham J D, Coop R L, Jackson F
Genetics and Behavioural Sciences Department, SAC, Edinburgh, UK.
Vet Parasitol. 1996 Feb;61(3-4):297-313. doi: 10.1016/0304-4017(95)00824-1.
Growing lambs (mean liveweight 22.4 kg) were used to test for the effects of long-term subclinical infection with Trichostrongylus colubriformis (2500 larvae per day) on the voluntary food intake (VFI), diet selection and performance of sheep given a choice between two foods of different protein content (low versus high). Sheep were either uninfected controls or parasitised for 27 weeks (Group 27P). Additional sheep were infected for either 9 or 18 weeks (before and after the development of complete resistance to parasites, as assessed by faecal egg counts) and then treated with anthelmintic to remove the parasites (Groups 9P and 18P). Group 18P remained uninfected after anthelmintic treatment whereas Group 9P was infected again for the last 9 weeks after a 9 week worm-free period. The VFI declined or remained static from Week 5 up to Week 11/12 of continuous infection, for the 27P and 18P groups. For 9P sheep, VFI recovered within a few days after the anthelmintic administration and was unaffected during re-infection over the last 9 weeks of the experiment. Diet selection changed in such a pattern that the proportion of the high protein food (prop H) in the selected diet started to increase from Week 6 of the infection. The prop H selected remained higher over the interval 10-18 weeks of the continuous infection for 27P and 18P groups than the uninfected controls. There were no significant differences in diet selection among any of the groups beyond Week 18 of the experiment. The infection caused a growth check from Week 7 to approximately Week 12/14 of dosing; these was no evidence of compensatory growth following the development of resistance or recovery. The results are consistent with the view that sheep given a choice between two appropriate foods will modify their diet selection in order to moderate the adverse effects of subclinical nematode infection. The performance and diet selection of all sheep beyond Week 18 of infection suggest that no obvious nutritional penalties are incurred with the continuation of the infection once the animals have become resistant to parasites.
选用生长中的羔羊（平均活重22.4千克）来测试长期亚临床感染蛇形毛圆线虫（每天2500条幼虫）对自愿采食量（VFI）、日粮选择以及在两种不同蛋白质含量（低蛋白与高蛋白）的食物之间进行选择的绵羊生产性能的影响。绵羊分为未感染的对照组或感染27周（27P组）。另外的绵羊感染9周或18周（通过粪便虫卵计数评估对寄生虫产生完全抗性之前和之后），然后用驱虫药驱虫（9P组和18P组）。驱虫处理后，18P组不再感染，而9P组在9周无虫期后在最后9周再次感染。对于27P组和18P组，连续感染的第5周到第11/12周期间，VFI下降或保持稳定。对于9P组绵羊，驱虫药给药后几天内VFI恢复，并且在实验的最后9周再次感染期间未受影响。日粮选择以这样一种模式变化，即所选日粮中高蛋白食物的比例（prop H）从感染第6周开始增加。对于27P组和18P组，连续感染的第10 - 18周期间所选的prop H高于未感染的对照组。实验第18周之后，各实验组之间的日粮选择没有显著差异。感染导致从给药第7周到大约第12/14周生长受阻；在产生抗性或恢复后没有补偿性生长的证据。这些结果与以下观点一致，即在两种合适食物之间进行选择的绵羊会改变其日粮选择，以减轻亚临床线虫感染的不利影响。感染第18周之后所有绵羊的生产性能和日粮选择表明，一旦动物对寄生虫产生抗性，继续感染不会产生明显的营养损失。
